Characterization and monitoring of reservoir flow barriers from pressure transient analysis for CO2 injection in saline aquifers

Abstract

Understanding of flow barriers in a saline aquifer evaluated for geological storage of carbon dioxide is the key point for decision making and designing injection operations. The barriers may significantly limit injection capacity, while their dynamic behavior during the operational phase, like fault reactivation and leakage out of the target formation, may cause unexpected completion of injection phase and have negative environmental consequences. The pressure data obtained in real-time during well testing and main phase of injection with installation of Permanent Downhole Gauges (PDG) may be utilized to characterize and monitor reservoir boundary conditions. Here, Pressure Transient Analysis (PTA) can be employed as interpretation tool.In this work, the case of faults acting as flow barriers including scenarios of sealing and leaking faults is studied using the history of CO2 injection into the Tubåen formation of the Snøhvit field as testing data set. The paper starts from answering general questions on applicability of PTA for CO2 injection, related to capabilities and limitations of single-phase flow models. It continues with suggesting and testing approximate approaches to improve the capabilities of such models to deal with CO2 injection cases (brine replica). Finally, an integrated workflow (or a technology, if combined with well surveillance system) for characterizing and monitoring flow barriers in geological storage projects is suggested. This workflow uses advantages of the models above for real-time data analysis. The paper concludes with recommendations for pre-injection well testing and surveillance during main injection phase, closing the loop with application guidelines.